1. Field of the Invention
The present invention relates to high speed dominant logic buses in communication systems that receive and transmit differential signals.
2. Description of Related Art
Buses are widely used to electrically connect two or more electronic devices. For example, a bus may be utilized to connect a printer, a monitor, and a keyboard with a CPU (Computer Processing Unit). Furthermore, buses are utilized within processors to connect various components of that processor, for example to connect memory with a particular processing unit.
In order to communicate between components, electrical signals are applied to the bus by a transmitting station and received by other stations on the bus. For high speed serial communication, a "differential" type of signal transmission has been found particularly advantageous. A differential signal is transmitted over a pair of wires. Each wire transmits the same signal, but with different polarities. A differential signal provides a higher signal to noise ratio, and better overall performance in part because timing distortions are minimized. The proposed IEEE 1394 Standard specifies a standard for a new high speed serial bus that transmits and receives differential signals over point-to-point links.
In addition to the type of signal transmitted on a bus, another design issue is the type of logic used by the bus: a "nondominant" logic or a "dominant" logic. In a dominant logic bus, one of the logic states is "dominant", which means that if any device places the dominant value on the bus, then the bus will assume that value. A dominant logic bus is particularly useful during arbitration in which more than one node can drive the bus at any time. For example, in a two-state dominant bus in which "high" is the dominant state, if at least one node drives the bus to a "high" state then all the nodes detect a "high" state on the bus. All the nodes detect a "low" state on the bus if and only if all the nodes drive the bus to the "low" state.
It would be an advantage to provide a bus circuit for high speed transmission of differential signals, and if the bus has a dominant logic. Such a bus could be useful for high speed communications, including use as a bus complying with the IEEE 1394 Standard.